It's difficult to tell without having it in hand, but it looks as if it might be element separation. It sticks out from the edge (or in towards the centre) in a semi-circular sort of fungus-like bump where your arrow points, but it also continues left and right around outer the edge of the front element as well. Regardless, if it's only at the outer edges, then it probably won't affect image quality, but it would bug the heck out of me. In similar circumstances, I generally send it back and keep looking.
I'd say separation as well. Way out at the very edge like this likely won't have an adverse affect on your images, but my concern would be the potential for it to get worse over time.
